Catalyst Heater Control Circuit (Bank 1)
The engine's computer detects a problem with the heater that warms up the catalytic converter on Bank 1, similar to a broken heating element in a space heater. This heater helps the converter work efficiently when the engine is cold.
The ECU monitors voltage and current flow through the catalyst heater circuit during cold starts and idle. It detects open circuits, shorts to ground, shorts to voltage, or excessive resistance that prevents the heater element from reaching proper operating temperature. The heater typically should draw current within a specific range when commanded on.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Heater Circuit Current | 8-15 amps (varies by vehicle) | Below 2 amps or above 20 amps, or no current draw |
| Heater Control Voltage | 12-14 volts when active | 0 volts or continuous high voltage without toggle |
Code P0429 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0429 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.